#!/usr/bin/node

const Readable=require('stream').Readable;

let c='a'.charCodeAt(0);


  


class MyReadable extends Readable{

  constructor(){
    super();
  }

  _read(){
    rs.push(String.fromCharCode(c++));
    if(c>'z'.charCodeAt(0)) rs.push(null);

  }
}


let rs=new MyReadable();

rs.pipe(process.stdout);
